What distributor are you using? Factory, aftermarket, etc???

I ask b/c the aftermarket MP ones did eventually adapt the Mallory mech. advance mechanism, which then meant you could use their Advance Curve Change Kit (part# 29014) to tailor accordingly.

I've had this in my setup for a number of years now, using 2 PINK springs which gives me 21 advance @ idle (800 RPM) and a full 35 at 2000 RPM.

Mallory of course makes their own line of Mopar SB distributors, but if I was to buy one now I would probably caugh up the $$$ for one of the programamble curve ones!

Take a look at the attached Curve Change Kit insturctions.